1. Field of the Invention
This invention has to do with precision measurement of the surface characteristics of work rolls which are used in the manufacture of sheet steel and other sheet metal products. More specifically, the invention relates to a non-contact method and apparatus for measuring the crown, taper, Ra (roughness average—measured in micro-inches in the English system and micrometers in the metric system), PPI (peaks per inch in the English system or peaks per centimeter in the metric system), traverse, chafter, body diameter, minor defects and inclusions of a work roll.
2. The Related Art
In the manufacture of sheet steel, sheet aluminum and other sheet metal products, paper, plastics and other sheet materials, steel work rolls are employed in the finishing process. The roll shape and surface are machined to a high degree of accuracy. The shape of the roll, e.g., contour and taper, requires measurements on the order of 1/10,000 inch which need to be accurate within ±3%. The surface texture, e.g., Ra and PPI, requires measurements on the order of 1/1,000,000 inch which need to be accurate within ±3%.
Current technology employs a profilometer or other mechanical contact measuring devices to take measurements of surface properties such as Ra and PPI but such devices do not provide acceptable accuracy, repeatability or resolution for measurement of the roll surface or topography. A moving caliper, for example, is mounted on small wheels and manually moved across the surface of the work roll. A needle or a mechanical probe is maintained in contact with the surface to take measurements. Several problems are associated with use of needles, mechanical probes and other devices which are maintained in contact with the roll because manual movement causes variations in readings. In the case of the moving caliper, the wheels come under stress when going toward or away from the crown on the roll, and the crown and taper of the roll cause the measurement to be taken along a path that is not a straight line.
A non-contact gauging apparatus and method for measuring the shape of rolls and controlling machine grinding operations is described in U.S. Pat. No. 5,800,247. The apparatus requires contacting the roll at least for initial positioning and it is mounted on the grinding machine and, therefore, subjected to machining vibration.
U.S. Pat. No. 4,423,636 describes a nondestructive eddy current or articulated probe mechanism which is automatically positioned over the test roll at the grinding wheel. The system is used to detect rolling mill roll surface defects for use with a defect test system.